Theory

Question 1

provides the majority of the optical power

Answer 1

air–tear-film interface

Question 2

measure the anterior corneal radius of curvature and estimate total

Answer 2

Standard keratometers and Placido-based

Question 3

Prolate shape - what means and how much

Answer 3

normal cornea flattens from the center to the periphery by up to 4.00 D. is flatter nasally

Question 4

changing the refractive status of the eye by 2.00 D

Answer 4

require altering the cornea’s thickness by less than 30 μm

Question 5

altering the cornea’s thickness by less than 30 μm

Answer 5

changing the refractive status of the eye by 2.00 D

Question 6

changing the refractive status - altering the cornea’s thickness how much

Answer 6

2.00 D - 30 μm

Question 7

most popular wavefront analysis

Answer 7

Hartmann-Shack

Question 8

lower-order aberrations

Answer 8

sphere (myopia, hyperopia) and cylinder (regular astigmatism)

Question 9

higher-order aberrations

Answer 9

spherical aberration, coma, and trefoil

Question 10

zero-order aberrations

Answer 10

lower-order - piston

Question 11

first-order aberrations

Answer 11

lower-order - vertical and horizontal prisms

Question 12

Myopia produces defocus

Answer 12

positive

Question 13

hyperopia produces defocus

Answer 13

negative

Question 14

Higher-Order Aberrations - when

Answer 14

pupil dilates, increase with age. particularly spherical aberration and coma, may increase after conventional surface ablation, LASIK, or RK for myopia

Question 15

Higher-Order Aberrations after corrections of hyperopia

Answer 15

ease even more than they do in myopic eyes but in the opposite (toward negative values)

Question 16

Most significant Higher-Order Aberration

Answer 16

Spherical aberration

Question 17

Spherical aberration - pathophysiology

Answer 17

peripheral light rays focus in front of more central rays

Question 18

Spherical aberration - symptoms signs

Answer 18

night myopia, halos around point images, increase depth of field but decreases contrast sensitivity

Question 19

Coma and trefoil - which worse

Answer 19

Coma

Question 20

Coma and trefoil - pathophysiology

Answer 20

rays at one edge of the pupil come into focus before rays at the opposite edge do. comet

Question 21

Coma - when

Answer 21

decentered corneal grafts, keratoconus, and decentered laser ablations

Question 22

Q value

Answer 22

degree of asphericity of the cornea

Question 23

Q for spherical corneas

Answer 23

Q = 0

Question 24

Q for prolate corneas (relatively flatter periphery)

Answer 24

Q <0

Question 25

Q for oblate corneas (relatively steeper periphery)

Answer 25

Q >0

Question 26

Q >0

Answer 26

oblate corneas (relatively steeper periphery)

Question 27

Q <0

Answer 27

prolate corneas (relatively flatter periphery)

Question 28

normal cornea Q value

Answer 28

–0.26

Question 29

overall corneal shape including spatial thickness profiles is best expressed by

Answer 29

computed tomography

Question 30

curvature (power) is best expressed by

Answer 30

Placido imaging

Question 31

topographic pattern in keratoconic eyes

Answer 31

inferonasal or inferotemporal steepening

Question 32

topographic pattern in PMD

Answer 32

inferior steepening, which is most dramatic between the 4 and 8 o’clock positions, with superior flattening. “crab-claw” shape

Question 33

oblate

Answer 33

steeper peripherally than centrally

Question 34

significant change in prescription for glasses or contact lenses

Answer 34

greater than 0.50 D in either sphere or cylinder within the past year